The present invention relates to a core drill, particularly of dry type, used for drilling through various concrete structures, asphalt, blocks, stone materials, rocks, tiles and the like.
A conventional core drill of such type generally comprises a base fixed to a concrete structure or the like by an anchor bolt, a pole provided upright from the base and formed with a rack, a drill head attached to the pole for vertical movement and containing a pinion that is engaged by the rack, a cylindrical core bit removably attached to the drill head, a motor with reduction gears provided in the drill head for rotatably driving the core bit and a handle for rotationally operating the pinion, wherein drilling through a concrete structure or the like is generally achieved by fixing the base to the concrete structure or the like by an anchor bolt, then pressing the handle, forcing the core bit against the concrete structure or the like, and applying a thrust while the core bit is rotated by driving the motor, and cooling water is applied, in most cases, to a drilled portion during a drilling operation.
Although the application of cooling water is for cooling a diamond tip that is fixed to a leading end of the core bit, allowing chips that are produced during the drilling operation to be discharged, and preventing dispersion of dusts, the vicinity of a drilled portion is submerged by the water. Thus, in such places where flooding of water is undesired as indoors, a water retaining pad is employed for circumferentially enclosing the concrete structure so that the water is retained within the pad, and prevented from flowing out. Even though such water retaining pad is employed, as soon as the drilling operation is completed, the cooling water flows out through the hole. For example, in the case a hole is drilled through a floor, as soon as the drilling operation is completed, the water flows out to the lower floor, and the lower floor is submerged by the water. In addition, such wet core drill using cooling water is difficult to be employed in drilling through a ceiling or a wall at a high position where retention of water is difficult, and cannot be used if such water supply facility as public water supply and water tank is unavailable.
A dry core drill adapted to achieve cooling of a diamond tip and discharge of chips by air injection to or air suction from a drilled portion, instead of using cooling water, is known.
A dry core drill with a vacuum suction device for allowing a diamond tip to be cooled and chips to be discharged by air suction within a core bit during a drilling operation is disclosed in Japanese Publication of Unexamined Patent Application No. Sho 58-49207, and a dry core drill with a swivel joint for introducing compressed air to a core bit so that cooling of a diamond tip and discharge of chips from a drilled portion are achieved by injection of the compressed air to the drilled portion is disclosed in Japanese Publication of Unexamined Utility Model Application No. Hei 7-2013.
In dry core drills, in addition to those of a fixed type that are fixed to a concrete structure or the like during a drilling operation, those of a handy type provided with a handle, and comprising a motor with a cooling fan and a core bit rotatably driven by the motor are also provided.
Although such dry core drill as described above is advantageous in that it can be used anywhere without limitation of an applicable range, as it requires no water supply facility and no retention of water, particularly in the case of such core drill of fixed type, as a drilling operation is continued, a drilling performance tends to be reduced, because chips produced by the drilling operation are built up between a surface of a diamond tip and a concrete structure or the like, and clogging is caused. On the other hand, in the case of a core drill of handy type, since vibrations caused by a drilling operation are directly transmitted to an operator, as a leading end of a core bit is forced against a concrete structure or the like by gripping a handle during the drilling operation, the controllability is poor.